This invention relates to overbased sulfonates, and more particularly to an improved process for producing calcium sulfonates with an enchanced filterability and reduced viscosity.
Calcium sulfonate additives are generally produced by carbonating a hydrocarbon solution of a "neutral" calcium sulfonate, a calcium base (usually calcium hydroxide and/or calcium oxide), and various reaction promoters including a low molecular weight alcohol (especially methanol), water and calcium chloride. During the overbasing process the calcium base is converted to calcium carbonate and incorporated into small inverted micellar structures. These basic calcium sulfonate micelles effectively allow the calcium base to be solubilized in an oil medium, i.e. the lubricating oil. The final product must be filtered to remove unreacted solids, particularly since an excess of the calcium base is typically utilized to prevent a phenomenon termed "overcarbonation" which results in an unacceptable product. The final product (typically a 50% oil concentrate) must also be fluid enough that it can be easily handled and blended into finished lubricant formulations.
Filterability and product viscosity are often the two primary concerns in developing an acceptable overbasing process, and a number of attempts to control these properties have been made and described. For example, U.S. Pat. No. 4,387,033 describes an overbasing process in which the reaction temperatures are carefully controlled and several carbonation stages are employed. In particular, the first carbonation step is carried out at 25.degree.-30.degree. C., and water is added as a critical ingredient. In addition, U.S. Pat No. 4,604,219 describes an overbasing process utilizing CaO as the base with a continuous and uniform addition of water over the entire carbonation period. It was found here also that the rate of water addition and the amount were critical to the production of a product with acceptable filterability and final viscosity.
Thus, it is an object of the present invention to provide a process for producing an overbased sulfonate having a better filterability and a reduced viscosity.